The invention relates generally to novel binding of therapeutic agents to albumin microbubble pharmaceuticals using an attachment of albumin affinity ligands to the agents. The binding provides a method of microbubble-assisted delivery of therapeutic agents to targeted cells or tissue of interest, either in vitro or in vivo.
Ultrasound-mediated destruction of microbubbles carrying drugs has been found to be useful as a noninvasive drug delivery system. Drugs or other therapeutic agents can be incorporated into the microbubbles in a number of different ways, including binding of the drug to the microbubble shell and attachment of ligands. For example, perfluorocarbon-filled microbubbles are sufficiently stable for circulating in the vasculature as blood pool agents; they act as carriers of these agents until the site of interest is reached. Ultrasound applied over the skin surface can then be used to burst the microbubbles at this site, causing localized release of the drug or therapeutic agents on site specific locations.
More specifically, albumin microbubbles have been used and delivered to a specific organ target by site-directed acoustic ultrasound. Albumin is a major protein in blood, and its natural physiological role is to bind and carry a wide variety of lipophilic/poorly soluble ligands throughout the body. These ligands, which may have an affinity to albumin, include fatty acids and other biosynthetic and catabolic products that are hydrophobic in nature. As such albumin microbubbles have been used to carry a variety of therapeutic agents based on proteins and other biologics including, oligonucleotides (ODN) and polynucleotides such as antisense ODN, with sequences complementary to a specific targeted messenger RNA (mRNA) sequence. These microbubble-nucleic acid complexes may be generated from unmodified ODN that are mixed with albumin or lipid components during microbubble shell formation or alternatively, the complex formation can be performed by mixing preformed microbubbles with an ODN of interest. In both cases, the ODN acts as a mechanistic intervention in the processes of gene translation or an earlier processing event. The advantage of this approach is the potential for gene-specific actions which should be reflected in a relatively low dose and minimal non-targeted side effects.
However, a key barrier to translating the potent biology of ODN into drugs is known to be at the level of drug delivery with efficacy and safety. For example, ODN delivery with chemical formulation, viral vectors, and particle delivery have been hampered with clinical safety related problems before therapeutic efficacy can be attained. Furthermore, the use of albumin microbubbles as a carrier of ODNs such as siRNA is limited due to the limited binding of the ODNs to the albumin microbubble as well as the stability of the albumin-ODN complex. Due to negative shell surface potential of albumin, the negatively charged shorter nucleic acids do not bind very well to the microbubble and gene transfection efficiencies using these complexes are generally suboptimal.
Thus there is a need to improve the binding of the therapeutic agents to the microbubble as well as improving the stability and efficacy of the microbubble complex.
Furthermore there is a need to reduce toxicity in the selective delivery of highly cytotoxic drugs. Non-targeted delivery of these drugs can cause systemic toxicity and has prevented the use of many of these drugs all together or at higher doses required for good efficacy. Attempts to deliver these as pro-drugs in many cases have reduced this problem, however, selective uptake in the targeted tissue is not always easy to achieve as most of the uptake mechanisms in the diseased tissue are also present in the normal tissue. Enhancing the uptake of these drugs in selective tissues by non-natural mechanisms as disclosed herein, therefore can add considerable value.